This invention relates to the manufacture of hydrogen peroxide.
Processes using anthraquinones for the production of H.sub.2 O.sub.2 operate on the basis of a cycle comprising hydrogenation, in the presence of a catalyst, of anthraquinones dissolved in a solvent; oxidation of the hydroanthraquinones which are thus obtained to produce hydrogen peroxide; and extraction of the H.sub.2 O.sub.2 generally by contact of water with the solution formed in the oxidation, the exhausted, or spent, solution being returned to the hydrogenation stage. It is known that these operations are accompanied by secondary reactions which transform the quinones into reduction products which do not generate hydrogen peroxide and these are designated "degraded substances" of the working solution. The consequence of this is a progressive reduction in the power of the solution to generate hydrogen peroxide. However, it is well known that this loss in power can be limited by introducing a supplementary operation, generally called "reconversion", into the operating cycle, the supplementary operation generally consisting in bringing all or part of the working solution into contact with a reconversion catalyst, this being effected continuously or intermittently, whereby some of the "degraded substances " are reconverted into active quinones, i.e. generators of H.sub.2 O.sub.2, which will be the anthraquinone being used or its nuclear hydrogenation derivative, the corresponding tetra-5,6,7,8-anthraquinone. However, generally some of the degraded substances are not reconverted into quinones, the reconversion reactions being too slow or the degradations being irreversible. Thus, the working solution is gradually enriched with "inert products", the concentration of which can reach a value which is prejudicial to the good functioning of the process.
There is in fact observed progressively a more rapid and more considerable soiling of the hydrogenation and reconversion catalysts, which is shown by an increased consumption of these latter materials, a soiling of the filters, and an accumulation of deposits at the interfaces of the H.sub.2 O.sub.2 solution and working solution during the extraction of the H.sub.2 O.sub.2. Analysis shows the presence, in these solutions, of polyanthracene compounds with a phenol function, which can be held responsible for the disadvantages referred to above. As well as these polyanthracene products, which can be designated as "heavy degraded products", there are other monoanthracene degradation products which can be designated "light degraded products". As the degraded products have the advantage of increasing the solubility of the quinones and especially of the hydroquinones, attempts have been made to free the working solution from the harmful part of said products, namely the "heavy degraded products". Different processes have been described, which comprise either chemical operations or physical operations or combinations of the two types of operation, but they frequently have the disadvantage that the process is complex and/or the disadvantage that secondary chemical reactions are involved in cases where chemical reagents are used.